Typically, moisturizing body washes contain both high levels of emollients (e.g., petrolatum, silicone and other such moisturizing ingredients), as well as surfactants to provide cleansing and rinsing properties.
Lamellar phase liquids (which contain alternating surfactant bilayers and water layers) are particularly desirable for use in high emollient liquids because they have a high zero viscosity (allowing them to stably support or suspend large amounts of emollient, for example), yet are shear thinning (readily disperse on pouring).
It should be understood that lamellar phases may be formed in a wide variety of surfactant systems using a wide variety of lamellar phase “inducers” as described, for example, in U.S. Pat. No. 5,952,286 titled “Liquid Cleansing Composition Comprising Soluble, Lamellar Phase Inducing Structurant” to Puvvada, et al. Generally, the transition from micelle to lamellar phase is a function of effective average area of head group of the surfactant, the length of the extended tail, and the volume of the tail. Using branched surfactants or surfactants with smaller head groups or bulky tails are also effective ways of inducing transitions from rod micellar to lamellar.
One way of characterizing lamellar dispersions includes measuring viscosity at low shear rate (using for example a Stress Rheometer) when additional inducer (e.g., lauric acid) is used. At higher amounts of inducer, the low shear viscosity will significantly increase. For purposes of the subject invention, the initial target viscosity (defined really to mean the viscosity after composition is left standing at 25° C. for one day) had to be greater than or equal to 80,000 cps, preferably at least 80,000 to 90,000 cps measured as defined in protocol.
Another way of measuring lamellar dispersions generally is using freeze fracture electron microscopy. Micrographs generally will show lamellar microstructure and close packed organization of the lamellar droplets (generally in size range of about 2 microns).
Although, when maintained at about room temperature (20-25° C.), lamellar liquids offer effective, stable compositions (having initial target viscosity, as noted, of at least 80K cps), these compositions may become unstable (e.g., through reduced viscosity and/or disruption of lamellar phase structures) when subjected to cold weather storage (e.g., 0-10° C. over two or more weeks) and/or to one or more freeze-thaw cycles. Thus, a further requirement of the invention was that final target viscosity (after cold storage and/or freeze-thaw tests) also be at least 80K cps. Preferably, both initial and final target viscosities, for purposes of the invention, is in the range of greater than or equal to 80K cps to 150K cps, preferably 80K to 140 cps, measured as defined in protocol.
In initial work, applicants discovered that, for purposes of compositions in which they are interested (maintaining viscosity, after heating to 50° C. for two weeks or more, at range of ≧80K cps, preferably 80K to 150K, preferably 80K to 140K cps; and maintaining stability, as defined by not phase separating), the presence of some amount of lauric acid (as viscosity modifier/lamellar phase inducer) was required. Initial viscosity should be at least 80K cps, preferably at least 90K cps (measured as defined in protocol). Upper limit is preferably less than or equal to 150K cps, more preferably lower than 140K cps. Balanced against this learning were applicants further learning during the course of work done on this application that keeping the amount of fatty acid (e.g., lauric acid) to a minimum (floor level) leads to enhanced emollient deposition, while using too much can lead potentially to viscosities out of noted final viscosity range. Thus, applicants found an unexpected ideal range where perfect balance is met.
During the course of their work on this application, applicants further discovered, and this is another aspect of the subject invention, that the addition of lauryl alcohol to compositions comprising ideal range of lauric acid, even in small amounts (e.g., 0.1-1.0% by wt.), significantly reduced the amount by which the initial viscosity was reduced (following freeze-thaw tests, as defined below) and/or actually increased viscosity compared to case where no lauryl alcohol was added. Thus, lauric acid and lauryl alcohol had unpredictable synergistic effect on freeze-thaw stability, and were one of required components that allowed compositions to be kept within required ranges.
However, to the extent there were still some freeze-thaw stability issues, applicants further unexpectedly discovered that specific combination of trihydroxystearin (oil phase or oil emollient structurant) with ideal range lauric acid and lauryl alcohol provided perfect combination to keep viscosity in required range (ideally 80-150K cps) after freeze-thaw stability tests.
Thus, as noted, the invention relates to specific combinations of lauric acid, lauryl alcohol and trihydrostearin in lamellar compositions having initial and final viscosity of at least 80,000 cps to 150K cps (final viscosity measured after cold weather storage and/or freeze-thaw stability tests).
To the extent any or all of these ingredients are disclosed for use in high emollient lamellar liquids, applicants are unaware of any disclosure where all three components must be selected in specifically defined ranges or recognition of their synergistic benefit.
As indicated, use of various techniques to enhance freeze-thaw stability in lamellar liquids is known (see U.S. Pat. No. 6,426,326 to Mitra et al.). Applicants are aware of no reference, however, which discloses the specific combination of lauric acid, lauryl alcohol and trihydroxystearin in specific ranges in such lamellar liquids, nor any recognition that use of this combination leads to maintaining viscosity within certain critically defined parameters both initially (e.g., after one day starting at 25° C.) and after various defined and rigorous stability tests.